1. Field of the Invention
The present invention relates to a ground fault detecting device for detecting ground fault of an ungrounded circuit installed in an electric vehicle or the like.
2. Description of the Related Art
In an electric vehicle (battery-powered vehicle, hybrid vehicle, fuel cell vehicle, or the like) including a direct-current power source which outputs high voltage, it is general to arrange the direct-current power source and a circuit connected to the direct-current power source as an ungrounded circuit insulated from a ground potential section of the vehicle body.
There has been conventionally proposed various configurations to detect ground fault in which the insulation of the ungrounded circuit arranged as such in the electric vehicle and the ground potential section of the vehicle body has lowered (a state of a resistance between the ungrounded circuit and the ground potential section of the vehicle is reduced close to 0 Ω) (for example, refer to Patent Document 1: Japanese Patent Application Laid-Open No. H08-226950, Patent Document 2: Japanese Patent No. 2933490, Patent Document 3: Japanese Patent Application Laid-Open No. 2009-150779, Patent Document 4: Japanese Patent No. 3590679).
In the configurations disclosed in the Patent Documents 1 to 3, since it is not able to detect a power supply voltage of the ungrounded circuit, it is necessary to prepare a voltage detector separate from a ground fault detector. Therefore, there is an inconvenience that the size of the ground fault detecting device increases when it is configured to perform ground fault detection and power supply voltage detection.
Furthermore, the configuration disclosed in Patent Document 4 divides the power supply voltage and applies output voltage of a reference power source to an intermediate potential, and detects ground fault based on flow of current from the reference power source to a ground fault resistance. According to this configuration, there is an inconvenience that ground fault cannot be detected since current does not flow when ground fault occurs with the same electric potential as the output voltage of the reference power source.